Receptors for the Fc portion of immunoglobulin are important in triggering many of the protective functions of monocytes, macrophages and polymorphonuclear cells. While receptors for IgG on these cells have been extensively investigated, it is becoming evident that receptors for IgA are also capable of promoting effector functions of these cells and that IgE may stimulate some activities of monocytes. While soluble IgA binds IgA receptor with poor avidity, polymerized IgA has been demonstrated to trigger functions such as superoxide generation and phagocytosis.